Turkish authorities probing the murder of an American woman in Istanbul are reportedly hunting for a homeless man who may have attacked her near the city's ancient walls on the day she disappeared. Istanbul police are searching for the man, identified only as "Z," in their investigation into the death of 33-year-old Sarai Sierra, of Staten Island, N.Y., whose body was found Feb. 2 near remnants of the city's ancient walls, according to the Turkish newspaper, Vatan.